1. Field of the Invention
The invention relates to a voltage supply apparatus, in particular for a radio telephone in a motor vehicle.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
A radio telephone which is permanently installed in a motor vehicle is normally supplied with power from the vehicle electrical system. It is thus connected to the vehicle electrical system such that the operating current for the radio telephone is supplied from the vehicle battery or from the generator, depending on the operating state of the vehicle electrical system. In this case, the supply voltage or supply voltages for the radio telephone, that is to say for the transmission radio-frequency amplifier and the rest of the telephone electronics, is or are taken from an appropriate power supply unit or a voltage matching circuit, on which the vehicle electrical system voltage from about 10 V to 16 V, if the rated voltage is 12 V, is present.
If the connection between the radio telephone and the vehicle electrical system is interrupted or if the vehicle battery is disconnected from the vehicle electrical system, then the voltage supply for the radio telephone thus fails, and telephoning is no longer possible.
Particularly if the vehicle electrical system fails as a result of an accident, in which the vehicle battery is ripped out or destroyed, it is desirable for the radio telephone still to be operable, at least for a certain time, in order to make an emergency call.
Proceeding from this, the invention is based on the object of providing a voltage supply apparatus for a radio telephone, in particular in a motor vehicle, which still allows telephone calls to be made, at least for a certain time, even in the event of failure of a main voltage source.